1. Field of the Invention
The present invention relates to optical signals, and more particularly optical communications.
2. Description of the Related Art
The advantages of optical fiber communication links are well known throughout the communications industry. Fiber optic communication links provide significant advantages over co-axial electrical communication links, and are virtually free from electromagnetic and radio frequency interference. Modern optical fibers offer low signal attenuation per kilometer, and high data-transmission rates with substantial bandwidth. Optic fibers possess an increased bandwidth over distance, which increases data communication distance for the same speed, and increased security from unauthorized tapping into the network. Additionally, several channels of information may be transmitted bidirectionally over a single fiber by, for example, Wavelength Division Multiplexing (WDM) and Dense Wavelength Division Multiplexing (DWDM) techniques.
In order to capitalize fully on the inherent advantages of optical signal transfer, many designers of optical networks believe that an all-optical system is the best objective to avoid numerous conversions to and from the electronic domain. The goal of all-optical signal processing can include the use of numerous switches, amplifiers, repeaters, and drop/add configurations for tapping into an optical network, along with the standard electronic conversion processes of generating and detecting optical radiation by lasers and photodetectors.
Optical switching has typically been a difficult process to achieve and manufacture, especially in a cost-effective manner. Throughout the years, several methods of switching optical signals have been proposed. In general, these switching technologies have been implemented utilizing a material""s nonlinear behavior, for example, by using its electro-optical, magneto-optical, or acousto-optic properties.
For electro-optical and magneto-optical switching, a material""s (e.g. lithium niobate and yttrium iron garnet, respectively) refractive index is altered by an external electric or magnetic field, respectively. These changes are typically microscopic alterations in the material""s birefringence that modify the polarization of the optical beam propagating through the media. Typically, this external field-induced birefringence in a material will alter the polarization of the propagating beam, and render the beam either transmitting or extinguished between crossed polarizers.
Acousto-optic devices depend on the material""s photo-elastic properties. In acousto-optic materials (e.g. tellurium dioxide, lithium niobate) an acoustic signal is propagated in the material producing a regular pattern of higher and lower refractive index regions, forming a Bragg diffraction grating. When coherent radiation is incident upon the activated material in the proper orientation, diffraction occurs at specific constructive angles. Typical Bragg angles are on the order of one degree, so an undesirable amount of horizontal spacing is required to separate the constructive angles far enough to allow accurate switching to occur. Additionally, the acoustically induced moving wave fronts can Doppler-shift the input beam frequency, presenting limitations in DWDM applications.
Another type of modulator or switching element is the polymeric or liquid crystal optical switch. These devices are similar to the electro-optic modulators in that polarization rotation occurs within the material under applied voltage. The liquid crystal or polymeric system is typically located between two polarizers, and the polarization rotation occurs due to the applied voltage activating long chain molecular interactions. An additional optical switch can be made using electro-holography in a photorefractive crystal. The beam is directionally guided by controlling the reconstruction process of volume holograms in the crystal (e.g. potassium lithium tantalate niobate) by means of an externally applied electric field using the quadratic electro-optic nonlinear effect.
Saturated absorption switches are another set of optical switches, performing incoherent as well as coherent optical switching. The process of saturated absorption usually occurs at higher optical powers (Watts/cm2), where the media goes from opaque to transparent when incident optical powers reach saturating levels, called critical optical powers. The saturation mechanism occurs as a result of the beam intensity itself, which changes the population of the material""s electronic energy levels to a non-thermal transmitting distribution. Saturated absorption has been used in the past for passive Q-switches in high power lasers.
Similar to the saturated absorption switch is the electro-absorption switching element. For electro-absorption switches, semiconductor band edges are manipulated in junction devices to modify the absorption edge wavelength. In this manner, a switch is constructed whereby incident radiation is either absorbed or reflected.
A new optical technology is applicable to all-optical, all-solid state components using dielectric material on substrate components for optical networks. The technology uses color centers along with active writing and erasing of the color centers for control of a device. Color center technology utilizes a linear optical effect that surpasses nonlinear (second order) phenomena, used presently in switching and routing components, in stability and controllability. In the past, color centers that were used in optical components permanently modified the optical structure and were not used as active controls of optical devices.
Although the above described methods of optical signal manipulation are possible, optical switches and routers having improved speed, higher efficiency and lower insertion loss are still desired for optical fiber communication links. An all-optical signal manipulation device is therefore desirable which is robust in operation, easy to manufacture, and cost effective.
An optical device comprises a signal input port, a first signal output port, a second signal output port, a controllable optical beam source, and a material susceptible to forming a plurality of radiation induced color centers. A refractive index change is induced in said material when illuminated with the controllable optical beam source so as to reflect an optical signal entering the optical device at the signal input port to the first signal output port when the controllable optical beam source is on, and so as to transmit the optical signal entering the optical device at the signal input port to the second signal output port when the controllable optical beam source is off.
An optical switch comprises a material susceptible to forming a plurality of radiation induced color centers, and a first controllable radiation source wherein a desired refractive index change is produced in the material when illuminated with the first controllable radiation source. The optical switch can further comprise a second controllable radiation source configured to erase the desired refractive index change.
An optical router comprises a plurality of signal input ports, a plurality of signal output ports, and a plurality of optical switches. The plurality of switches comprises a first controllable optical beam source, and a material having a plurality of radiation induced color centers such that a reflective optical structure is formed in the material when illuminated with the first controllable optical beam source so as to reflect an optical signal entering at least one of the plurality of signal input ports to at least one of the plurality of signal output ports.
A method of altering the propagation direction of an optical signal comprises receiving the optical signal on a surface of a material susceptible to forming a plurality of radiation induced color centers, and inducing a refractive index change in the material by illuminating the material with a controllable radiation source.
An optical switch comprises a plurality of layers, wherein at least one layer is made of a material which is susceptible to forming radiation induced color centers, and a first controllable radiation source wherein a desired refractive index change is produced in the at least one layer with the first controllable radiation source.
A method of altering the propagation direction of an optical signal comprises passing the optical signal through a material, and inducing color centers in a portion of the material to create a first portion of the material having a first index of refraction and a second portion of the material having a second index of refraction, whereby the optical signal is reflected at an interface between the first portion and the second portion.
An optical switch comprises a block of material having an optical signal input port and an optical signal output port, a light source positioned to illuminate a surface of the block of material, and a mask covering a portion of the surface.